Description

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1917 edition. Excerpt: ...dentition is lost before birth. Only a few fishes (adult Acipenser, Coregonus, etc.) lack teeth, while in most they extend to the lining bones of the mouth and in Fig. 239.--Jaws of a six month lion, after Weber. Milk teeth white. permanent dotted. i, incisors;-c, canines; m, molars; p, premolars. some to the hyoid and branchial arches (pharyngeal bones). Usually they are conical, but they may be flattened and pavement-like or even form large plates, apparently by the coalescence of numbers of primitive teeth (dipnoi). In the amphibians the teeth are not so widely distributed in the mouth, occurring on the margins of the jaws and on the palatines and vomers, rarely on the parasphenoid, while they are entirely lacking in Bufo and Pipa. Among the reptiles the turtles and some of the pterodactyls are toothless; most of the others have the teeth confined to the margin of the jaws, though they occur on the palatines and pterygoids in the snakes and lizards, and rarely (Sphenodon) on the vomer. While the conical shape prevails, the teeth present a great variety of forms, some of the theriomorphs closely simulating the mammals in their heterodont dentition. The teeth may be anchylosed to the summit of the jaws (acrodont); applied to their inner side (pleurodont, fig. 106, d); or have their roots implanted in grooves or sockets or alveoli (thecodont). Mention must also be made of the poison fangs of certain serpents. These are specialized teeth borne on the maxillary bones and are either permanently erect (proteroglypha) or the bone may turn, as on a pivot, so that when the mouth is closed the teeth lie Fig. 240.--Poison gland and fang of rattlesnake, Crotalus horridus (Princeton 1404). p, poison gland; /, labial glands. along the roof of the mouth, but...show more